1. Field of the Invention
The present invention relates to a rotor identification system for a centrifuge instrument.
2. Description of the Prior Art
A centrifuge instrument is a device by which a sample of a liquid is exposed to a centrifugal force field. The sample is carried within a centrifuge rotor. The rotor is mounted at the top of a rotatable shaft that is connected to a source of motive energy.
A centrifuge instrument may accept any one of a plurality of different centrifuge rotors, depending upon the separation protocol being performed. Accordingly, for both speed and temperature control considerations, it is advantageous to be able to ascertain the identity of the particular rotor mounted within the instrument during a given run. Such rotor identification information is further advantageous from a safety standpoint, since access to such information prevents operation of the rotor at a speed in excess of the rotor's maximum design speed or at an energy level in excess of the maximum containment energy of the instrument.
Various rotor identification arrangements are known. U.S. Pat. No. 5,037,371 (Romanauskas), assigned to the assignee of the present invention, discloses and claims a rotor recognition system that utilizes an ultrasonic transmitter and receiver to interrogate a rotor mounted within the instrument and to generate a rotor identification signal. With this arrangement the rotor itself does not carry any identifying indicia, aside from the identification information inherently present in its shape.
Other rotor identification systems modify each rotor used in the instrument to the extent that one or more detectable elements are disposed in some predetermined position on the body of the rotor. In some rotor identification systems the detectable elements take the form of individual magnets arranged in a predetermined pattern on the rotor. Magnetically responsive detectors are mounted in appropriate corresponding positions in the instrument. U.S. Pat. No. 4,772,254 (Grassl) exemplifies this class of identification system. In other rotor identification systems a coded disc having a pattern of alternating light reflective and light absorptive regions is attached to the rotor. Each reflective or absorptive region defines a detectable element. Corresponding optical transmitter/receiver devices are appropriately positioned within the instrument. U.S. Pat. No. 4,205,261 (Franklin) exemplifies this class of identification system.
In either class of identification system the identity of a given rotor may be based either upon the angular distance (with respect to the axis of rotor rotation) between two selected detectable elements or upon the number and/or type (e.g., polarity, reflectivity) of detectable elements passing a given detector during a predetermined time period. However, each basis in which rotor identity is determined is believed to exhibit attendant disadvantages.
In a rotor identification system that depends upon the angular distance between detectable elements it is possible that two rotors may have the same maximum speed and the same included angle. However, the rotors may have different optimum control parameters for speed and/or temperature and different kinetic energy levels at top speed. It would therefore be advantageous if each rotor was able to be uniquely identified.
In a rotor identification system that depends on the number and/or type of detectable elements on the rotor, a missing detectable element or a malfunctioning detector may result in a rotor mis-identification. This could result in non-optimum speed and/or temperature control parameters or even a safety hazard if the rotor is permitted to exceed either its design speed or the containment energy level of the centrifuge containment system. A malfunctioning sensing detector can also lead to these same problems.
In view of the foregoing it is believed advantageous to provide a rotor identification system that avoids the possibility of such rotor mis-identification and the effects of sensor malfunction.